Context Manipulation with .apply and .call

context_man.js

var obj1 = {
    num : 4
}

function multiply(val){
    return this.num * val;
}

console.log(multiply(3)); //impossible because no num defined in window (NaN)
console.log(multiply.apply(obj1, [4])); //16
console.log(multiply.call(obj1, 4)); //16